The present invention relates generally to apparatus for detecting emission levels of air pollutants, and more particularly, is directed to a smoke opacity detector.
The Federal Clean Air Act requires all companies having exhaust stacks to restrict the amount of visual emissions therefrom to a specific range. The Environmental Protection Agency (EPA) sets the standards for complying with this Act. If a company fails to comply with this requirement, it may be subject to sanctions including fines, mandated installation of air pollution control equipment, and legal actions to prevent the company from operating. In addition, various state environmental laws of a similar nature are enforced by state environmental agencies.
As an example, in the specific application of a textile finishing operation, solvents or chemicals are used which are subjected to very high temperature conditions. As a result thereof, smoke (gas containing particulate impurities) is produced and emitted into the atmosphere.
Various devices are known which test the amount of smoke from a material.
For example, in U.S. Pat. No. 3,544,218 to Cassidy, a specimen which is held by a specimen holder in a burning chamber is burnt by an ignition flame from a gas burner nozzle. The amount of the flame and heat required for different materials being tested can be varied. Smoke collected in the chamber is exhausted through an exhaust duct into a smoke detecting device having a light unit and a photoelectric cell. However, because a gas burner nozzle is used, it is difficult to control the heat to an exact temperature. Further, the smoke must travel out of the chamber into a separate conduit, which may affect the final measurement due to dispersement of the gas. It is further noted that the EPA has determined that water vapor is not a contaminant. Accordingly, in many situations, the effects of water vapor on the smoke detector should be eliminated. However, with Cassidy, there are no means for taking into account conditions for water vapor.
U.S. Pat. No. 3,973,852 to Moore et al discloses a method and apparatus for measuring particulate concentration in the atmosphere. However, Moore et al does not burn a sample and measure smoke opacity, but rather, only measures atmospheric pollution at a particular location using a laser light beam and a receiver. Moore et al does discuss the need to eliminate conditions of water vapor. This is accomplished, however, by a complex arrangement using monochromatic laser pulses.
U.S. Pat. No. 5,110,214 to Battiste et al discloses an apparatus for evaluating the propensity of polymers for smoking during processing, that is, for measuring the smoke emitted when the polymer is melted and extruded. The temperature for burning the gases is controlled by heater bands, although it is stated that an automated melt indexer or other rheometer may be used to melt and extrude the polymer. The gases that are burned from the sample are supplied through a side arm opening and tube to an aerosol monitor for analysis of smoke content. The smoke content in the monitor is determined by any of a plurality of different disclosed light detecting means. The output from the smoke detector is compared with known values for known compositions and/or different particle sizes. However, there is no control provided to take into account the effects of water vapor.
U.S. Pat. No. 5,220,179 to Gagea discloses an apparatus for detecting the presence of vapor and/or smoke in the outgoing air of a device for heating materials. Specifically, the smoke from a sample in a microwave unit travels to an exhaust pipe. Light from a light source is either transmitted (unobstructed) to a light receiver, absorbed by the smoke particles or reflected by the vapor particles to the light receiver. In this manner, water vapor conditions can be controlled. Therefore, the detection of water vapor in the smoke is determined by the reflected light. However, besides being a complex arrangement to account for water vapor, Gagea does not eliminate water vapor from the smoke to be detected, but rather, must provide a separate determination.
U.S. Pat. No. 5,163,332 to Wong discloses a gas sample chamber connected at one end to a source chamber which contains a small incandescent lamp or other light source and at the other end is connected to a detector. Wong shows heater wires attached to the outside of the tube of the gas sample chamber and which prevent condensation of water vapor on the inside of the tube. However, Wong uses specular reflection along the walls of the chamber, and is therefore only concerned with water vapor condensing on the walls in small droplets, rather than water vapor being present in the gas itself. Also, Wong is not concerned with smoke detection, but rather, only with gas analysis, and for this reason, Wong specifically keeps dust and smoke particles out of the sample chamber by a sheet of semi-permeable membrane that functions as a filter.
Other patents of interest are U.S. Pat. No. 5,092,674 to Garner and U.S. Pat. No. 5,148,234 to Tamm et al.